Drug substances may be delivered into a patient's body via injection into the muscle, subcutaneous tissue, or into the epidermis and dermis (also referred to as an intradermal injection). The efficacy of a particular drug substance may change when the drug is delivered intradermally. In some cases, intradermal delivery may be more beneficial to the patient. There is considerable variation in the skin thickness both between individuals and within the same individual at different sites of the body. Generally, the outer skin layer epidermis has a thickness of ranging from 50 to 200 microns, and the dermis, the inner and thicker layer of the skin, has a thickness ranging from 1.5 to 3.5 mm. Therefore, a needle cannula that penetrates the skin deeper than about 3 mm has a potential of passing through the dermis layer of the skin, thus making the injection into the subcutaneous region, which may result in an insufficient immune response, especially where the substance to be delivered intradermally has not been indicated for subcutaneous injection. Also, the needle cannula may penetrate the skin at too shallow a depth to deliver the substance and result in what is commonly known in the art as a “wet injection” due to reflux of the substance from the injection site.
The standard procedure for making an intradermal injection, generally referred to as the Mantoux procedure, is difficult to perform, and successful administration of an intradermal injection using that procedure depends upon experience and technique of the person using the injection device. The Mantoux procedure requires that the user of the injection device stretch the skin, orient the needle bevel to face upwardly, and insert a 26 gauge short bevel needle cannula to deliver a volume of 0.5 ml or less of the drug substance into the skin of the patient. During this procedure, the needle cannula must be maintained at an angle varying from around 10° to 15° with respect to the patient's skin to form a blister or wheal in which the drug substance is deposited or otherwise contained. The above-described technique is difficult to perform and typically requires the attention of a trained nurse or medical doctor. Inserting the needle to a depth greater than about 3 mm typically results in a failed intradermal injection because the drug substance being expelled through the cannula will be injected into the subcutaneous tissue of the patient.
As disclosed in United States Patent Application Publication No. 2002/0068909 A1, which published on Jun. 6, 2002, and U.S. Pat. No. 6,494,865 B1, which issued on Dec. 17, 2002, both to the assignee herein, an intradermal needle assembly has been developed for use with a prefillable container having a reservoir capable of storing a drug substance for injection into the skin of a patient. A needle cannula is supported by the prefillable container and has a forward tip extending away from the container. The intradermal needle assembly includes a limiter that is securable to the prefillable container and which surrounds the needle cannula and provides a generally flat skin engaging surface extending in a plane generally perpendicular to an axis of the needle cannula. The flat skin engaging surface is adapted to be received against the skin of the patient during administration of the intradermal injection. The needle forward tip extends beyond the skin engaging surface a distance of approximately 0.5 to 3 mm. Therefore, the limiter limits penetration of the needle into the dermis layer of the skin of the patient so that the drug substance is injected into the dermis layer of the patient.